Twin impeller drive for jet pump

Abstract

A jet propulsion unit for a watercraft that employs a pair of counter rotating impellers that are disposed immediately adjacent each other so that the need for straightening vanes is eliminated. The impellers are driven by a bevel gear transmission to rotate in opposite directions, which bevel gear transmission is contained within the jet propulsion unit outer housing but forwardly of the flow path of water therethrough. This bevel gear transmission is driven by a single input shaft through a flexible coupling.

I claim: 
     
       1. A jet propulsion unit for a watercraft comprised of an outer housing comprising a water inlet portion through which water may be drawn from a body of water in which the watercraft is operating and a discharge nozzle portion through which the water is discharged for generating a propulsion force to the watercraft, a pair of impellers positioned between said water inlet portion and said discharge nozzle, and transmission means disposed forwardly of said impellers and out of the path of water flow through said water inlet for driving said impellers in opposite directions for pumping water from said water inlet to said discharge nozzle, said transmission means including a pair of telescoped shafts, each affixed to a respective one of said impellers within said jet propulsion unit, the inner of said telescoped shafts being journalled at its rear end within said outer housing, the outer of said telescoped shafts being journalled within said outer housing upon said inner telescoped shaft. 
     
     
       2. A jet propulsion unit for a watercraft as in claim 1, wherein straightening vanes are not positioned between the impellers. 
     
     
       3. A jet propulsion unit for a watercraft as in claim 2, wherein there no straightening vanes are provided in the discharge nozzle. 
     
     
       4. A jet propulsion unit for a watercraft as in claim 1, wherein the transmission means comprises a bevel gear transmission. 
     
     
       5. A jet propulsion unit for a watercraft as in claim 4, wherein the bevel gear transmission drives the telescoped impeller drive shafts. 
     
     
       6. A jet propulsion unit for a watercraft as in claim 5, wherein the impeller shafts comprise a tubular impeller shaft driven directly by one of said bevel gears for driving the forwardmost impeller and a second solid impeller shaft passing through said tubular impeller shaft and driving the aftmost impeller. 
     
     
       7. A jet propulsion unit for a watercraft as in claim 6, wherein the bevel gear transmission is disposed forwardly of and adjacent the water inlet portion and further including forward bearings contiguous to the water inlet portion for journaling the impeller shafts relative to each other and relative to the outer housing. 
     
     
       8. A jet propulsion unit for a watercraft as in claim 7, wherein the non-tubular impeller shaft extends forwardly through the outer housing for connection to a driving shaft for driving of the transmission, the bevel gear transmission further including an idler bevel gear supported for rotation about an axis extending transversely to the impeller shaft axes and disposed in an upper portion of the outer housing. 
     
     
       9. A jet propulsion unit for a watercraft as in claim 1, further including a single prime mover for driving the transmission through a flexible coupling. 
     
     
       10. A jet propulsion unit for a watercraft as in claim 9, wherein the transmission means comprises a bevel gear transmission. 
     
     
       11. A jet propulsion unit for a watercraft as in claim 10, wherein the bevel gear transmission drives the telescoped impeller drive shafts. 
     
     
       12. A jet propulsion unit for a watercraft as in claim 11, wherein the impeller shafts comprise a tubular impeller shaft driven directly by one of said bevel gears for driving the forwardmost impeller and a second solid impeller shaft passing through said tubular impeller shaft and driving the aftmost impeller. 
     
     
       13. A jet propulsion unit for a watercraft as in claim 12, wherein the bevel gear transmission is disposed forwardly of and adjacent the water inlet portion and further including forward bearings contiguous to the water inlet portion for journaling the impeller shafts relative to each other and relative to the outer housing. 
     
     
       14. A jet propulsion unit for a watercraft as in claim 13, wherein the non-tubular impeller shaft extends forwardly through the outer housing for connection to a driving shaft for driving of the transmission, the bevel gear transmission further including an idler bevel gear supported for rotation about an axis extending transversely to the impeller shaft axes and disposed in an upper portion of the outer housing. 
     
     
       15. A jet propulsion unit for a watercraft as in claim 14, wherein straightening vanes are not provided between the impellers. 
     
     
       16. A jet propulsion unit for a watercraft as in claim 15, wherein there are provided no straightening vanes in the discharge nozzle.